The present invention relates to a semiconductor junction laser which employs an InP substrate, and more particularly to a semiconductor junction laser structure for fundamental transverse mode oscillation.
For continuous oscillation of a semiconductor laser at room temperature, use must be made of a laser structure which confines an injected current and light energy within a radiation region of the active layer. To this end, a stripe electrode type semiconductor laser was proposed in which its electrode is stripe-shaped to prevent the injected current from flowing into other portions than the radiation region. However, this conventional semiconductor laser has a drawback such that even if the stripe is narrowed, the injected current path widens in the active layer to provide an insufficient current confinement effect, making the fundamental transverse mode oscillation impossible.
To overcome this defect, a buried hereto (hereinafter referred to simply as BH) type semiconductor laser was proposed.
However, this laser element has such defects as follows: Firstly, the active layer once obtained by crystal growth is also subjected to etching. By this etching, the InGaAsP is exposed in either side wall of the active layer and it is not clear how this exposed portion is grown by the second crystal growth; it is considered naturally that lattice defects are liable to occur in such an interface. This is a problem which must be solved for enhancement of reliability. Another defect is a technical difficulty in appreciable reductions of the thickness and width of the active layer which are required for the fundamental transverse mode oscillation because of too large a difference between the refractive indexes of the active layer and the surrounding InP layers, i.e. 3.51 and 3.17. Moreover, even if this problem could be solved, there would be posed another drawback of small light output. In fact, the light output obtainable with the existing BH arrangement is as small as several to ten-odd milliwatts.